The cause of psoriasis isn't fully understood, but it's thought to be related to an immune system problem with T cells and other white blood cells, called neutrophils, in your body.
T cells normally travel through the body to defend against foreign substances, such as viruses or bacteria.
But if you have psoriasis, the T cells attack healthy skin cells by mistake, as if to heal a wound or to fight an infection.
Overactive T cells also trigger increased production of healthy skin cells, more T cells and other white blood cells, especially neutrophils. These travel into the skin causing redness and sometimes pus in pustular lesions. Dilated blood vessels in psoriasis-affected areas create warmth and redness in the skin lesions.
The process becomes an on-going cycle in which new skin cells move to the outermost layer of skin too quickly — in days rather than weeks. Skin cells build up in thick, scaly patches on the skin's surface, continuing until treatment stops the cycle.
Just what causes T cells to malfunction in people with psoriasis isn't entirely clear. Researchers believe both genetics and environmental factors play a role.
Psoriasis typically starts or worsens because of a trigger that you may be able to identify and avoid. Factors that may trigger psoriasis include: